An agricultural seeding machine such as a row crop planter or grain drill places seeds at a desired depth within a plurality of parallel seed trenches formed in soil. In the case of a row crop planter, a plurality of row crop units are typically ground driven using wheels, shafts, sprockets, transfer cases, chains and the like or powered by electric or hydraulic motors. Each row crop unit has a frame which is movably coupled with a tool bar. The frame may carry a main seed hopper, herbicide hopper and insecticide hopper. If a herbicide and insecticide are used, the metering mechanisms associated with dispensing the granular product into the seed trench are relatively simple. On the other hand, the mechanisms necessary to properly meter the seeds, and dispense the seeds at predetermined relative locations within the seed trench are relatively complicated.
The mechanisms associated with metering and placing the seeds generally can be divided into a seed metering system and a seed placement system which are in series communication with each other. The seed metering system receives the seeds in a bulk manner from the seed hopper carried by the planter frame or by the row unit. Different types of seed metering systems may be used, such as seed plates, finger plates, seed disks, etc. In the case of a seed disk metering system a seed disk is formed with a plurality of seed cells spaced about the periphery of the disk. Seeds are moved into the seed cells with one or more seeds in each seed cell depending upon the size and configuration of the seed cell. A vacuum or positive air pressure differential may be used in conjunction with the seed disk to assist in movement of the seeds into the seed cell. The seeds are singulated and discharged at a predetermined rate to the seed placement or delivery system.
The most common seed delivery system may be categorized as a gravity drop system. In the case of the gravity drop system, a seed tube has an inlet end which is positioned below the seed metering system. The singulated seeds from the seed metering system merely drop into the seed tube and fall via gravitational force from a discharge end thereof into the seed trench. The seed tube may have a rearward curvature to reduce bouncing of the seed as it strikes the bottom of the seed trench and to impart a horizontal velocity to the seed in order to reduce the relative velocity between the seed and the ground. Undesirable variation in resultant in-ground seed spacing can be attributed to differences in how individual seeds exit the metering system and drop through the seed tube. The spacing variation is exacerbated by higher travel speeds through the field which amplifies the dynamic field conditions. Further seed spacing variations are caused by the inherent relative velocity difference between the seeds and the soil as the seeding machine travels through a field. This relative velocity difference causes individual seeds to bounce and tumble in somewhat random patterns as each seed comes to rest in the trench.
Various attempts have been made to reduce the variation in seed spacing resulting from the gravity drop. U.S. Pat. No. 6,681,706 shows two approaches. One approach uses a belt with flights to transport the seeds from the meter to the ground while the other approach uses two belts to grip the seed and transport it from the meter to the ground. While these approaches control the seed path and reduce variability due to dynamic events, neither approach seeks to deliver the seed with as small as possible horizontal velocity difference relative to the ground. U.S. Pat. Nos. 6,651,570, 7,185,596 and 7,343,868 show a seed delivery system using a brush wheel near the ground to regulate the horizontal velocity and direction of the seed as it exits the seeding machine. However, there is still a gravity drop between the seed meter and the brush wheel which produces variation in seed spacing.